An overview on photocatalytic sulfate radical formation via doped graphitic carbon nitride for water remediation

Nanomaterials-Induced Redox Imbalance: Challenged and Opportunities for Nanomaterials in Cancer Therapy

Cancer cells typically display redox imbalance compared with normal cells due to increased metabolic rate, accumulated mitochondrial dysfunction, elevated cell signaling, and accelerated peroxisomal activities. This redox imbalance may regulate gene expression, alter protein stability, and modulate existing cellular programs, resulting in inefficient treatment modalities. Therapeutic strategies targeting intra- or extracellular redox states of cancer cells at varying state of progression may trigger programmed cell death if exceeded a certain threshold, enabling therapeutic selectivity and overcoming cancer resistance to radiotherapy and chemotherapy. Nanotechnology provides new opportunities for modulating redox state in cancer cells due to their excellent designability and high reactivity. Various nanomaterials are widely researched to enhance highly reactive substances (free radicals) production, disrupt the endogenous antioxidant defense systems, or both. Here, the physiological features of redox imbalance in cancer cells are described and the challenges in modulating redox state in cancer cells are illustrated. Then, nanomaterials that regulate redox imbalance are classified and elaborated upon based on their ability to target redox regulations. Finally, the future perspectives in this field are proposed. It is hoped this review provides guidance for the design of nanomaterials-based approaches involving modulating intra- or extracellular redox states for cancer therapy, especially for cancers resistant to radiotherapy or chemotherapy, etc.

Activation of persulfate by biochar-supported sulfidized nanoscale zero-valent iron for degradation of ciprofloxacin in aqueous solution: process optimization and degradation pathway

The pollution of antibiotics, specifically ciprofloxacin (CIP), has emerged as a significant issue in the aquatic environment. Advanced oxidation processes (AOPs) are capable of achieving stable and efficient removal of antibiotics from wastewater. In this work, biochar-supported sulfidized nanoscale zero-valent iron (S-nZVI/BC) was adopted to activate persulfate (PS) for the degradation of CIP. The impacts of different influencing factors such as S/Fe molar ratios, BC/S-nZVI mass ratios, PS concentration, S-nZVI/BC dosage, CIP concentration, initial pH, coexisting anions, and humic acid on CIP degradation efficiency were explored by batch experiments. The results demonstrated that the highest degradation ability of S-nZVI/BC was achieved when the S/Fe molar ratio was 0.07 and the BC/S-nZVI mass ratio was 1:1. Under the experimental conditions with 0.6 g/L S-nZVI/BC, 2 mmol/L PS, and 10 mg/L CIP, the degradation rate reached 97.45% after 90 min. The S-nZVI/BC + PS system showed significant degradation in the pH range from 3 to 9. The coexisting anions affected the CIP degradation efficiency in the following order: CO32- > NO3- > SO42- > Cl-. The radical quenching experiments and electron paramagnetic resonance (EPR) revealed that oxidative species, including SO4•-, HO•, •O2-, and 1O2, all contribute to the degradation of CIP, in which •O2- plays a particularly prominent role. Furthermore, the probable degradation pathway of CIP was explored according to the 12 degradation intermediates identified by LC-MS. This study provides a new idea for the activation method of PS and presents a new approach for the treatment of aqueous antibiotics with highly catalytic active nanomaterials.

Sulfate Radical in (Photo)electrochemical Advanced Oxidation Processes for Water Treatment: A Versatile Approach

The search for a simple and clean approach toward the production of sulfate radicals for water treatment gave rise to electrochemical and photoelectrochemical activation techniques. The photoelectrochemical activation method does not just distinguish itself as a promising activation method, it is also used as an efficient water treatment method with the ability to treat a myriad of pollutants due to the complementary effects of highly reactive oxidizing species. This perspective highlights some merits that distinguish sulfate monoanion radicals from hydroxyl radicals. It highlights the electrochemical, photoelectrochemical, and in situ photoelectrochemical routes of generating sulfate radicals for advanced oxidation process approach to water treatment. We provide a detailed account of the few known applications of sulfate radical enhanced photoelectrochemical treatments of water laden with organics. Finally, we placed this area of research in perspective by providing outlooks and conclusive remarks.

Peroxydisulphate activated FTO-WO3 nanorods based photoelectrocatalytic degradation of tetracycline: Intermediate products, degradation pathway and ecotoxicity studies

This work reports sulphate radical assisted photoelectrocatalytic (SR-PEC) degradation of tetracycline using a visible light active fluorine-doped tin oxide - tungsten trioxide nanorods (FTO-WO3 NRs) photoanode. The WO3 NRs were synthesised via the hydrothermal method and then conducted on the FTO glass to form a photoanode. When the photoanode was applied without sulphate radicals for PEC degradation, 10 % of the tetracycline was degraded. Conversely, when 3 mM persulphate was added, the extent of tetracycline degraded was 88 % using the UV-vis spectrophotometer and 99 % using the ultra-performance liquid chromatography mass spectrometer (UPLC-MS) within 90 min at 1.5 V. The mechanism of tetracycline degradation was proposed based on the intermediate products identified using UPLC-MS and the extent of toxicity was evaluated using quantitative structure activity relationship (QSAR) analysis. Trapping experiment revealed that the photogenerated holes, sulphate radicals, and hydroxyl radicals were the oxidants that significantly took part in the degradation of tetracycline. Overall, the electrode was stable and reusable, therefore suggesting the suitability of FTO-WO3 NRs photoanode in the presence of sulphate radicals towards the decontamination of water laden with pharmaceutical pollutants.

Oxygen doped graphite carbon nitride as efficient metal-free catalyst for peroxymonosulfate activation: Performance, mechanism and theoretical calculation

In this study, oxygen-doped graphitic carbon nitride (g-C3N4), named O-g-C3N4, was successfully fabricated and characterized, and its performance in activating peroxymonosulfate (PMS, HSO5-) for the removal of phenol, 2,4-dichlorophenol (2,4-DCP), bisphenol A (BPA), rhodamine B (RhB), reactive brilliant blue (RBB) and acid orange 7 (AO7) was evaluated. The catalytic performance of O-g-C3N4 for AO7 removal increased by 14 times compared to g-C3N4. In the presence of 0.2 g L-1 O-g-C3N4, 3.5 mM PMS at natural pH 5.8, 96.4% of AO7 could be removed in 60 min, reduced toxicity of the treated AO7 solution was obtained, and the mineralization efficiency was 47.2% within 120 min. Density functional theory (DFT) calculations showed that the charge distribution changed after oxygen doping, and PMS was more readily adsorbed by O-g-C3N4 with the adsorption energy (Eads) of -0.855 kcal/mol than that of the pristine g-C3N4 (Eads: -0.305 kcal/mol). Mechanism investigation implied that AO7 was primarily removed by the sulfate radicals (SO4•-) and hydroxyl radicals (•OH) on the surface of O-g-C3N4, but the role of singlet oxygen (1O2) to AO7 elimination was negligible. The results of cyclic experiments and catalyst characterization after reaction confirmed the favorable catalytic activity and structural stability of O-g-C3N4 particles. Furthermore, the O-g-C3N4/PMS system was very resistant to most of the environmental impacts, and AO7 removal was still acceptable in natural water environment. This study may provide an efficient metal-free carbonaceous activator with low dosage for PMS activation to remove recalcitrant organic pollutants (ROPs).

Fabrication and characterization of novel, cost-effective graphitic carbon nitride/Fe coated textile nanocomposites for effective degradation of dyes and biohazards

Textile-based photocatalysts are the new materials that can be utilized as an effective sustainable solution for biochemical hazards. Hence, we aimed to develop a sustainable, cost-effective, and facile approach for the fabrication of photocatalytic fabric using graphitic carbon nitride (g-C3N4) and ferric-based multifunctional nanocomposite. Bulk g-C3N4 was prepared from urea by heating it at 500 °C for 2 h. The structure of ball-milled g-C3N4 was engineered by doping with various amounts of iron (III) chloride hexahydrate solution (0.006 mol/L) and sintered at 90 °C for 24 h to prepare g-C3N4-nanosheets/α-Fe2O3 composites. These nanocomposites have potential avenues towards rational designing of g-C3N4 for improved photocatalytic, antibacterial, and antiviral behavior. The prepared nanocomposite was characterized for its surface morphology, chemical composition, crystal structure, catalytic, antibacterial, and antiviral behavior. The fabrication of ferric doped g-C3N4 nanocomposites was characterized by SEM, EDX, FTIR, and XRD analysis. The coated fabric nanocomposite was characterized for methylene blue dye degradation under visible light, antibacterial and antiviral behavior. The developed textile-based photocatalyst has been found with very good recyclability with photocatalytic degradation of dye up to 99.9 % when compared to conventional g-C3N4 powder-based photocatalyst.

Sulfate radicals-based advanced oxidation processes for the degradation of pharmaceuticals and personal care products: A review on relevant activation mechanisms, performance, and perspectives

Owing to the rapid development of modern industry, a greater number of organic pollutants are discharged into the water matrices. In recent decades, research efforts have focused on developing more effective technologies for the remediation of water containing pharmaceuticals and personal care products (PPCPs). Recently, sulfate radicals-based advanced oxidation processes (SR-AOPs) have been extensively used due to their high oxidizing potential, and effectiveness compared with other AOPs in PPCPs remediation. The present review provides a comprehensive assessment of the different methods such as heat, ultraviolet (UV) light, photo-generated electrons, ultrasound (US), electrochemical, carbon nanomaterials, homogeneous, and heterogeneous catalysts for activating peroxymonosulfate (PMS) and peroxydisulfate (PDS). In addition, possible activation mechanisms from the point of radical and non-radical pathways are discussed. Then, biodegradability enhancement and toxicity reduction are highlighted. Comparison with other AOPs and treatment of PPCPs by the integrated process are evaluated as well. Lastly, conclusions and future perspectives on this research topic are elaborated.